Record-low temperatures have blanketed about two-thirds of the U.S. this week, and while the extreme cold weather seems to have finally broken, it left many people wondering why these frigid temps are happening.

Atmospheric scientist Jennifer Francis theorizes that the reason for the very cold snap in the middle of the country is due to a large dip south in the jet stream, a very fast-moving river of air that controls the weather experienced in the mid-latitudes. Francis said a person's position in relation to the waves of the jet stream, such as the north-south undulations in the stream, determines what the weather conditions are.

Furthermore, scientists believe that the warming of the Arctic area brought about by climate change is contributing to changes in the jet stream, causing the extremes many Americans experienced this week. She indicated that the Arctic region is warming as much as two to three times the rate of the rest of the northern hemisphere.

“The difference in the temperature between the Arctic and areas farther south is getting smaller. The reason that’s important is because it’s that temperature difference that fundamentally drives the jet stream in the first place,” she said. “That means the west to east winds in the jet stream are weakening because that driving force behind them is getting weaker. And we know that when the jet stream winds weaken, it tends to meander north and south more, and we tend to see these big swings like we’ve seen this week.”

Francis said this isn't just happening here in the U.S. She mentioned the meandering jet stream has contributed to much warmer winter weather in Alaska and Scandanavia.